1. Field of the Invention
The present invention relates to a display apparatus, and more particularly to a Liquid Crystal Display device (“LCD”) driven by thin film transistors (“TFT”) formed on a substrate.
2. Description of the Related Art
Generally speaking, a display apparatus is a kind of an interface device that makes images defined by information sources to be visually perceivable to human beings.
Many types of display devices are known, including LCD (Liquid crystal Display), PDP (Plasma Display Panel), and OLED (Organic Light Emitting Diode). All these are flat panel displays. In particular, liquid crystal displays (LCD) are widely used for laptop computers, desktop monitors, and televisions because of their superior resolution, color capabilities, and overall display quality.
An LCD may include two panels provided with field-generating electrodes such as pixel electrodes and a common electrode, and a liquid crystal (LC) layer interposed therebetween. The LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer. The electric field determines the orientations of LC molecules in the LC layer to adjust the polarization of incident light.
The LCD includes a plurality of thin film transistors (TFT) connected with the pixel electrodes and also includes a plurality of signal lines connected with the TFTs, such as gate lines and data lines.
One known LCD type is a vertically aligned (VA) LCD, in which LC molecules are aligned such that their long axes are perpendicular to the panels in the absence of an electric field. The VA LCD offers a high contrast ratio and a wide reference viewing angle. The reference viewing angle is defined as a viewing angle with the contrast ratio equal to 1:10 (the contrast ratio is the luminosity ratio between the darkest and brightest colors).
The viewing angle of the VA mode LCD can be increased, for example, by providing suitable cutouts or protrusions in the field-generating electrodes. The cutouts and the protrusions cause the tilt angles of the LC molecules to spread in different directions such that the reference viewing angle can be widened.
However, the cutouts and the protrusions decrease the aperture. Also, the lateral visibility of the VA mode LCD is low. For example, images displayed by a patterned vertically aligned (PVA) LCD equipped with the cutouts become brighter as the viewing angle increases, making it harder to tell the difference between different bright colors.
In order to improve lateral visibility of an LCD, a variety of methods have been suggested which involve dividing a pixel electrode into a pair of sub-pixel electrodes, driving the sub-pixel electrodes with different voltages using different thin film transistors (TFT), and using a coupling capacitor that changes the voltage of one but not both of the sub-pixel electrodes of a pixel.